The present invention relates to structures within a camera, and more specifically, to the internal structural arrangement of a single lens reflex (SLR) camera.
Generally, SLR cameras have at least one internal skeleton or chassis. One such chassis is commonly known as a camera body, and is a unitarily formed structure that includes a cartridge chamber, a spool chamber, and a rear plate having guide rails with an aperture frame formed therein. Usually, the camera body is made of diecast aluminum or another metal, in order to provide sufficient rigidity to maintain optical alignments and to help support large lenses. However, when the camera body is formed from metal, the camera is heavy.
Recently, the performance of engineering plastics has improved, and these plastics have gradually been used to form more parts in camera assemblies. However, the camera body usually remains metal, as it bears significant mechanical loads and provides important reference surfaces for alignment.
FIG. 1 shows an exploded view of internal parts of a conventional SLR camera 100, while FIG. 2 shows a side sectional view of the conventional camera 100 as assembled. As shown in FIG. 1, the main structural members of the conventional camera 100 are a camera body 13, a supporting plate 12, a shutter block 15, and a mirror box 14.
The supporting plate 12 is secured to the bottom of the camera body 13 by screws 116a, 116b, and 116c, via holes 121a, 121b, and 121c of the supporting plate and threaded holes 134a, 134b, and 134c of the camera body 13, respectively. The shutter block 15 has mounting tabs 151a, 151b formed at a top portion thereof, and is secured (via holes 152a, 152b in the mounting tabs and threaded holes 133a, 133b in the camera body) to the upper portion of the camera body 13 by screws 118a, 118b. Further, the shutter block 15 is secured to the lower portion of the camera body by a screw 118c, via a hole 152c in the shutter block and a threaded hole 133c in the camera body 13.
As illustrated in FIGS. 1 and 2, the shutter block 15 comprises front and rear shutter frames, shutter blades 153b, a blade chamber 153 wherein the shutter blades 153b are accommodated, and a driving mechanism (not shown) for driving the blades 153b. The blade chamber 153 is provided between the shutter frames. The shutter block 15 carries out exposure control by driving the shutter blades 153b when taking a photograph. An opening 153a is formed in the rear of the shutter block 15 to allow light to pass to the film, and a corresponding opening is formed in the front of the shutter block 15.
The camera body 13 has top mounting blocks 131a, 131b integrally formed therein, while the mirror housing 14 has matching mounting blocks 141a, 141b integrally formed therein. The mirror housing 14 is secured to the top portion of the camera body 13 (over the shutter block 15) by screws 119a, 119b, via holes 132a, 132b in the top mounting blocks 131a, 131b and threaded holes 142a, 142b in the matching mounting blocks 141a, 141b, respectively. The bottom of the mirror housing 14 is secured to the supporting plate 12 by screws 117a, 117b, passing via holes 121d, 121e in the supporting plate and threaded holes 142c, 142d in the mirror housing. A threaded tripod socket 115 for engaging a tripod or other supporting device is provided on the supporting plate 12.
The camera body 13 of the conventional camera is formed with a cartridge chamber 136, a spool chamber 137, and a thin back plate 135 between the two chambers 136 and 137. An aperture frame 135a, which defines the exposable area of a film in the camera, is formed in the back plate 135. Film is loaded in the finally assembled conventional camera by placing a film cartridge, in the cartridge chamber 136 and drawing the film across the aperture frame 135a to a winding spool (not shown) in the spool chamber 137.
To stabilize the position and transport of the film, the thin back plate 135 of the conventional camera body 13 is provided with a pair of integrally formed inner rails 161a, 161b and a pair of integrally formed outer rails 162a, 162b. During photography and film transport, the film is flattened against the inner rails 161a, 161b and guided between the outer rails 162a, 162b.
Decorative cover portions 122, shown by a phantom line in FIG. 2, are provided on the top, front and bottom of the camera 100. As shown in FIGS. 1 and 2, a body side bayonet mount 19 is provided on the front (the photographing lens side) of the camera 100, and is secured to the mirror housing 14 by a screw 19a. A lens side bayonet mount is provided on the lens barrel of a compatible photographing lens (not shown), and is mountable to the body side mount 19.
A quick return mirror, including a main mirror 111 and a sub mirror 112 (shown by phantom lines in FIG. 2) is accommodated in the mirror housing 14. The quick return mirror is swingably supported by the mirror housing 14 to swing between a photographing position and a observing position. The position illustrated by phantom lines in FIG. 2 is the observing position, where incident light is divided by the main mirror 111 into reflected light and passing light. The reflected light is directed upwards to a focusing screen, pentamirror, and finder (not shown). The passing light is reflected by the submirror 112 to an autofocus detection system (not shown). The quick return mirror moves to its photographing position when a release switch (not shown) is turned ON. To reach the photographing position, the main mirror 111 and submirror 112 are flipped up parallel to the focusing screen, and incident light passes to the shutter block 15. Subsequently, the shutter block 15 is activated to carry out the exposure onto a film.
As shown in FIG. 2, a back lid 17 is closable to the rear of the camera body 13. Grooves 13a and 13b are provided at the rear side of the camera body 13 to accept the upper and lower rims of the back lid 17 when the back lid 17 is shut, shielding the back of the camera 100 against the intrusion of light. On the inner side of the back lid 17 (inside the camera 100 when the back lid 17 is closed), a pressing plate 18 is resiliently supported by supports 18a for pressing the film into a position against the inner rails 161a, 161b and between the outer rails 162a, 162b.
The thin back plate 135 can be affected by externally applied stresses, which is one reason why the camera body 13 is conventionally made of metal. If the thin back plate 135 is distorted by an externally applied stress, the aperture frame 135a, and the rails 161a, 161b, 162a, and 162b are consequently distorted, adversely affecting the image quality.
When the conventional camera 100 is attached to a tripod, a large externally applied bending force can directly transmit from the tripod socket 115 through, for example, the screw 116b to the thin back plate 135. This can cause the back plate 135 to warp, making the film flatness (controlled by the inner rails 161a, 161b), position (controlled by the outer rails 162a, 162b), and image shape (controlled by the aperture frame 135a) poor.
A body thus fabricated as the conventional camera body 13, having the inner rails 161a, 161b and outer rails 162a, 162b, and frame aperture 135a formed in the thin back plate 135, is sensitive to externally applied forces. Furthermore, if the camera body is made of plastic, the conventional camera structure as described, including the camera body 13, supporting plate 12, shutter block 15, and mirror housing 14, then the camera would be even more subject to distortion when external forces are applied.